Method and Apparatus for Dual Porting a Single Port Serial Ata Disk Drive

1. An apparatus for providing a plurality of ports to a device using a point to point communications protocol, comprising: a first data port, wherein said first data port is adapted for interconnection to said device; a second data port; a first signal path, wherein said second data port may be selectively interconnected to said first data port by said first signal path; a third data port; and a second signal path, wherein said third data port may be selectively interconnected to said first data port by said second signal path, wherein data is passed over said first signal path in a first mode of operation, wherein data is passed over said second signal path in a second mode of operation, wherein a portion of said first signal path is also a portion of said second signal path, wherein said first mode of operation is entered in response to at least one of a command and data received at said second data port, and wherein at least one of a command and data is prevented from being passed over said second signal path until at least one of a command and data is received from said device at said first data port in reply to said at least one of a command and data received at said second data port.

2. The apparatus of claim 1 , wherein a queue tag is associated with commands and data passed over said first and second signal paths, wherein communications having a first queue tag value are passed over said first signal path, and wherein communications having a second queue tag value are passed over said second signal path.

3. The apparatus of claim 1 , further comprising: a first host interconnected to said first signal path; and a second host interconnected to said second signal path, wherein at least one of a command and data is passed between said device and said first host over said first signal path in said first mode of operation, and wherein at least one of a command and data is passed between said device and said second host over said second signal path in said second mode of operation wherein said first signal path is not operative to interconnect said first and second data ports while a transfer of a command or data using said second signal path is pending, and wherein said second signal paths is not operative to interconnect said first and third data ports while a transfer of a command or data using said first signal path is pending.

4. The apparatus of claim 3 , wherein said first host comprises a first controller and wherein said second host comprises a second controller.

5. The apparatus of claim 3 , wherein said first host comprises a first RAID controller, and wherein said second host comprises a second RAID controller.

6. The apparatus of claim 1 , wherein said device comprises a storage device.

7. The apparatus of claim 1 , wherein said device comprises a single port device.

8. The apparatus of claim 1 , wherein said device comprises an SATA device.

9. The apparatus of claim 3 , further comprising a RAID system back plane wherein said first signal path is interconnected to said first host by a first back plane signal path, and wherein said second signal path is interconnected to said second host by a second backplane signal path.

10. A data storage system, comprising: a first device controller; a second device controller; a plurality of data storage devices, wherein each of said data storage devices requires point to point connection; a plurality of switch assemblies, wherein each of said switch assemblies comprises at least first, second, and third data ports, wherein said switch assemblies operate to selectively interconnect said first port to one of said at least second and third ports, and wherein for each of said switch assemblies only one of said second and third ports is interconnected to a one of said data storage devices while a transfer of a command or data through said first port is pending; a backplane, comprising: interconnections to said at least second and said third ports of said switch assemblies; and an interconnection to said first device controller, an interconnection to said second device controller; a plurality of first backplane signal paths, wherein said first device controller may communicate with a second port of any of said switch assemblies; and a plurality of second backplane signal paths, wherein said second device controller may communicate with a third port of any of said switch assemblies.

11. The data storage system of claim 10 , wherein said first device controller comprises a RAID contoller, and wherein said second device controller comprises a RAID controller.

12. The data storage system of claim 10 , wherein said data storage devices comprise SATA data storage devices.

13. The data storage system of claim 10 , further comprising a plurality of carriers, wherein a one of said data storage devices and a one of said switches is interconnected to each of said carriers.

14. A method for providing point to point communications between a plurality of hosts and a device, comprising: establishing a first communication channel between said device and a first of said hosts in response to a communication received from said first host; passing at least one of a command and data between said device and said first host over said first communication channel; and establishing a second communication channel between said device and a second of said hosts in response to a communication received from said second host, wherein said device is incapable of operation on a shared bus, wherein said first and second communications channels are established by a switch assembly having a plurality of states, comprising: a first state, wherein communications between said device and said first host are enabled, wherein communications between said device and said second host are disabled, and wherein said first state is maintained at least until a communication is received by said switch from said device in reply to said communication from said first host; and a second state, wherein communication between said device and said second host are enabled, wherein communications between said device and said first host disabled, and wherein said second state is maintained at least until a communication is received from said device in reply to said communication from said second host.

15. The method of claim 14 , further comprising: preventing establishment of a communication channel between said device and said second host in response to a communication received from said second host while a transfer of at least one of a command and data over said communication channel between said device and said first host is pending.

16. The method of claim 14 , further comprising: passing at least one of a command and data from said device to said first host over said first communications channel.

17. The method of claim 14 , wherein said states of said switch assembly further comprise: a third state, wherein no communications between said device and said first and second hosts are enabled.

18. The method of claim 14 , wherein said first state is maintained until no transfer of at least one of a command and data between said device and said first host are pending.

19. The method of claim 14 , wherein said switch assembly enters said second state in response to a communication from said second host.

20. The method of claim 14 , wherein in response to at least one of a command and data received at said switch assembly from said second host while said switch assembly is in said first state and while a transfer of at least one of a command and data between said device and said first host is pending no ready signal is passed from said switch assembly to said second host, wherein said at least one of a command and data from said second host is not passed to said device.

21. The method of claim 14 , wherein at least one of a command and data having an associated first queue tag is passed between said device and said first host, and wherein at least one of a command and data having an associated second queue tag is passed between said device and said second host.

22. The apparatus of claim 1 , wherein only said first data port is adapted for interconnection to said device.